1. Field of Invention
This invention relates to ink jet printers and more particularly, to a method of achieving efficiency by utilizing two-dimensional resolution enhancement and thinning of a pixel image using priority masks.
2. Description of Related Art
An ink jet printhead selectively ejects droplets of ink from a plurality of drop ejectors to create a desired image on an image receiving medium such as paper. The printhead typically comprises an array of drop ejectors that convey ink to the image receiving medium. In a carriage-type, ink jet printhead, the printhead moves back and forth relative to the image receiving medium to print the images in swaths.
The ink jet printhead typically comprises a plurality of ink passageways such as capillary channels. Each channel has a nozzle end and is connected to an ink supply manifold. Ink from the manifold is retained within each channel until in response to an appropriate signal applied to a resistive element in that channel, the ink in a portion of the channel adjacent to the heating element is rapidly heated and vaporized. Rapid vaporization of some of the ink from the channel creates a bubble that causes a quantity of ink (i.e., an ink droplet) to be ejected through the nozzle to the image receiving medium. U.S. Pat. No. 4,774,530 to Hawkins, the disclosure of which is incorporated herein by reference, shows a general configuration of a typical ink jet printer.
Many commercially available ink jet printers have a 300 dots per inch (dpi) resolution along the horizontal axis (also called the raster scan axis) and a 300 dpi resolution along the vertical axis so as to form round individual ink droplets that form the pixel images on the paper. These ink jet printers are therefore designed to print 300xc3x97300 dpi output images. However, increased resolution is desired to print higher resolution images and thus visually pleasing images. For example, it may be desirable to print a pixel image at a 300xc3x97600 dpi effective resolution using a 300 dpi ink jet printhead or a 600xc3x97600 dpi effective resolution using a 300 dpi ink jet printhead. This resulting image would therefore appear to be printed with a higher resolution.
U.S. Pat. No. 5,270,728 to Lund et al., the disclosure of which is incorporated herein by reference, discloses a method of multiplying the speed resolution of a raster scanning device such as an ink jet printer. A 300xc3x97600 dpi pixel image is mapped to a corresponding, nonoverlapping physical dot image and the ink jets are fired in response to the dot image to direct ink droplets onto the printer at a 600 dpi resolution grid timing to effectively double the horizontal resolution of the pixel image.
U.S. Pat. No. 5,270,728 describes thinning the pixel image before it is printed by selectively turning OFF pixels within the pixel image by referencing the edges of the pixel image. More specifically, U.S. Pat. No. 5,270,728 describes a method of maintaining selected ones of the pixels in an ON state based on ON pixel adjacency and edge proximity criteria. In U.S. Pat. No. 5,270,728, the pixel image that is initially received is a 300xc3x97600 dpi image. The described method thins the pixel image so as to print at the resolution of the printhead.
However, it may also be desirable to increase the resolution of a 300xc3x97300 dpi pixel image to have the visible appearance of a higher resolution. Particularly, it may be desirable to print the pixel image at a 300xc3x97600 dpi effective resolution or even better yet at a 600xc3x97600 dpi effective resolution. This results in enhancing the curves on edges of the image.
U.S. Pat. No. 5,029,108 to Lung, the disclosure of which is incorporated herein by reference, teaches a method of enhancing edge representations when an image is converted from graphical format to print format. Edges are modified by repositioning related dots or by altering the dot size. A TBAP (To Be Adjusted Pixel) located on an edge is modified to enhance the smoothness of a segment transition. Gradient mask matrices are used to determine whether a change of brightness occurs.
U.S. Pat. No. 4,437,122 to Walsh et al., the disclosure of which is incorporated herein by reference, teaches a method of enhancing the resolution and quality of characters. A pixel pattern is formed including a center pixel and neighboring pixels.
The pixel pattern is compared with standard pixel patterns and the center pixel may be altered based on the standard pixel pattern that the current pixel pattern matches.
U.S. Pat. No. 5,742,300 to Klassen, the disclosure of which is incorporated herein by reference, discloses a method of printing an image having a 300xc3x97600 dpi effective resolution with an ink jet printer that has a 300 dpi resolution. The method increases a resolution or density of the pixel image along the raster scan axis. The pixel image is thinned and raster scanned with the ink jet printer to visibly reproduce the pixel image at the 300xc3x97600 dpi resolution. The pixel image may be thinned based on a checkerboard pattern while maintaining and enhancing edges.
U.S. Pat. No. 5,677,714 to Klassen et al. the disclosure of which is incorporated herein by reference, discloses a method of printing an image having a 600 dpi resolution along a horizontal axis with an ink jet printer that has a 300 dpi resolution. The disclosed method maintains the edges of the pixel image and uses a checkerboard pattern for all interior pixels other than the second pixel and the second last pixel at each pixel row. Thus, the method is neighbor insensitive by using a checkerboard pattern or mask to determine the state of the interior pixels. After turning OFF the respective pixels, ink drops are fired from the ink jet printer at areas corresponding to the remaining ON pixels to visibly reproduce the image at the 600 dpi resolution along the horizontal axis.
Other prior art resolution enhancement methods may print excessive amounts of ink on the copy sheet which causes the ink to run and distort the image. Furthermore, the ink jet should have the ability to generate drops at such a high frequency when a grid timing of the pixel is altered.
This invention may provide a method of two-dimensional resolution enhancement and thinning preferably by altering a 300xc3x97300 dpi image to produce a 600xc3x97600 bitmap image and then thinning the bitmap image using priority masks prior to printing on an image receiving medium. Other resolutions such as 400 and 800 dpi are also within scope of this invention.
The invention may provide a method for printing a pixel image using a ink jet printer having a first resolution along a first axis and a second resolution along a second axis transverse to the first axis. The method may include receiving the pixel image having the first resolution along the first axis and the second resolution along the second axis. The method may then increase the resolution of the pixel image along the first axis and the second axis. The method may then alter edges of the pixel image and thin the pixel image using priority masks. Then, the method may raster scan the thinned pixel image with the ink jet printer to visibly reproduce the pixel image at the increased resolution.
This summary of the invention is in no way meant to limit the scope of the present invention but rather is a brief summary of at least one aspect of the invention. Other objects, advantages and salient features of the invention will become apparent from the detailed description taken in conjunction with the annexed drawings, which disclose preferred embodiments of the invention.